// https://leetcode-cn.com/problems/reverse-string/

public void ReverseString(char[] s)
{
    if (0 == s.Length)
        return;
    char tmp;
    for (int i = 0, j = s.Length - 1; i < j; i++, j--)
    {
        tmp = s[i];
        s[i] = s[j];
        s[j] = tmp;
    }
}